The present invention relates to a sensor and more particularly to a gas sensor such as an oxygen sensor, HC sensor and NOx senor, for detecting a gas component in a gas and a temperature sensor for detecting the temperature of a gas.
It is heretofore known a gas sensor having such a structure in which a sensor element formed at a forward end with a detection portion for detecting a gas component in a gas is disposed inside a metallic casing. The metallic casing is constituted by a plurality of coaxial tubular members such as a metallic housing formed at an outer circumferential surface thereof with a threaded portion for installation of a sensor, a protector connected to the metallic housing in such a manner as to cover the detection portion of the sensor element, which protrudes from the forward end of the metallic housing, an inner tubular member connected to a rearward open end portion of the metallic housing and covering a portion of the sensor element, which extends rearward from the rearward open end portion, and an outer tubular member radially surrounding an outer circumferential periphery of the inner tubular member while interposing therebetween a water repellant filter.
Such a gas sensor (e.g., oxygen sensor) is installed on, for example, an exhaust pipe of an exhaust system of an automotive engine or the like. Further, it is recently a general practice to provide the exhaust pipe with a catalytic device for decomposing a toxic substance in an exhaust gas and dispose a gas sensor downstream of the catalytic device thereby measuring a detection component in an exhaust gas from which a toxic substance has been removed. In this instance, since the gas sensor is disposed downstream of the exhaust pipe that extends rearward from the engine and along the bottom of a vehicle body, water drops or the like may adhere to the outer surface of the gas sensor. Accordingly, in order to prevent the water drops or the like from entering into the gas sensor, it is important for the plurality of tubular members to be joined assuredly together for attaining the water tightness of the gas sensor.
Crimping is known as a method of joining the plurality of tubular bodies together. For example, it is known a gas sensor in which a protector is fixed to a forward end of a metallic housing by crimping, a forward end of an inner tubular member is fixed to a rearward end of the metallic housing by crimping, a forward overlying portion of the outer tubular member, which overlies on the inner tubular member, is fixed to the inner tubular member by crimping as disclosed in Unexamined Japanese Patent Publication No. 11-352095. In this sensor, the outer tubular member is formed at the forward side with a crimping section (crimped fixing section) in the form of an annular recess extending circumferentially there around, i.e., decreased in diameter so as to allow the forward end of the crimping section to fittingly engage the outer surface of the inner tubular member, thereby closing a space between the inner tubular member and the outer tubular member. Accordingly, by forming such crimping sections at predetermined places, a single-piece tubular body having a high water tightness can be obtained.